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• Monitor file in Java on Linux 64bits

  - by Tim

  I'd like to be notified when a file has been created, deleted or changed, but not using polling mechanism. I have surveyed related Java API that can use.(EX:JNotify, JPathWatch and JXFileWatcher) Those APIs provide file monitor by using native component on OS. But I met the same problem is that they can't run on Linux 64bits, because native component in those APIs donen't support Linux 64bits, and this confused me for a long time. I also know that there'll be a WatchService API as part of NIO2 in JDK7, but JDK7 has not released yet. So, can any one suggest me a better solution? Very Thanks.

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• Detect insertion of media into a drive using windows messages

  - by rschnorenberg

  I am currently using WM_DEVICECHANGE to be notified when new USB drives are connected to the computer. This works great for devices like thumb-drives where as soon as the device arrives it is ready to have files read from it. For devices like SD card readers it does not because the message is sent out once when the device is connected but no message is sent when a user actually inserts a card into the device. Is it possible to detect the insertion of new media into an existing USB device without having to use polling?

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• How to make/monitor/deploy daemon processes in JRuby

  - by nazdrug

  I'm currently porting a Rails App currently using REE to JRuby so I can offer an easy-to-install JRuby alternative. I've bundled the app into a WAR file using Bundler which I'm currently deploying to GlassFish. However, this app has a couple of daemon processes and it would be ideal if these could be part of the WAR file, and potentially monitored by Glassfish (if possible). I've looked at QuartzScheduler, and while meets my needs for a couple of things, I have a daemon process that must execute every 20 seconds as it's polling the database for any delayed mail to send. If anyone can provide any insight as to how best to set up daemon processes in a JRuby/Java/Glassfish environment any help will be greatly appreciated! :)

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• Intentionally get a "MySQL server has gone away" error

  - by Jonathan

  I'm trying to cope with MySQL's error MySQL server has gone away in a django env. The quick workaround was to set the global wait_timeout MySQL variable to a huge value, but in the long run this would accumulate to many open connections. I figured I'll get the wait_timeout variable and poll the server in smaller intervals. After implementing this I tried to test it but am failing to get the error. I set global wait_timeout=15 and even set global interactive_timeout=15 but the connection refuses to disappear. I'm sure I'm polling the database in larger intervals than 15sec. What could be the cause for not being able to recreate this error?

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• Connection Timeout Extension/Detection

  - by ircmaxell

  Well, let me start off by explaining what I'm trying to do. I have an application that stalls a HTTP connection until new data is available (sometimes a few seconds, sometimes 30 minutes or so). Right now, the system works fine if the data is sent within a few minutes. The problem I'm facing, is that it doesn't seem that XHR recognizes a dropped connection... So instead of killing the current connection and reconnecting when it detects a dropped connection, it just sits there. I'd really not like to have it force-reconnect every minute or two (That's one reason this app was written, to stop the need for polling). So, my questions are as follows: Is there a way to detect a dropped (not closed) TCP connection with XHR? Is there a way that I can tell XHR not to timeout (I saw IE8 has the .timeout property) Would it be better to send a header (or some other content) every now and then (say once per minute) down the pipe to keep the connection open? Thanks.

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• Temporarily disabled NSArrayController filterPredicate, or consult ManagedObjectContext?

  - by ndg

  I have an NSArrayController which is bound to a class in my Managed Object Context. During runtime the NSArrayController can have a number of different filter predicates applied. At certain intervals, I want to iterate through my NSArrayController's contents regardless of the filter predicate applied to it. To do this, I set the filterPredicate to nil and then reinstate it after having iterated through my array. This seems to work, but I'm wondering if it's best practice? Should I instead be polling my Managed Object Context manually? NSPredicate *predicate = nil; predicate = [myArrayController filterPredicate]; [myArrayController setFilterPredicate:nil]; for(MyManagedObject *object in [myArrayController arrangedObjects]) { // ... } [myArrayController setFilterPredicate:predicate];

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• What's your favorite programmable calculator?

  - by Pat Notz

  The HP-32S still holds a soft spot in my heart, even though it only had 4 registers. I have fond memories of writing a nonlinear solver for finding an azeotrope curve during a Thermodynamics final. Despite the increase in power, memory, pixels and features the HP-32G that followed never could steal my heart away. Here's to you, HP-32S. Let's hear it, what's your favorite programmable calculator? As with all poll type questions, do NOT submit a new answer unless your answer is not represented. Vote up your answer instead of adding yet another TI-85 or HP-49 to the list, and add comments to that answer if you want to relate specifics. EDIT: I moved my photo into an answer for polling.

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• Is there an example of checking on if a WCF Service is online?

  - by apolfj

  I will have a client application using a proxy to a WCF Service. This client will be a windows form application doing basicHttpBinding to N number of endpoints at an address. The problem I want to resolve is that when any windows form application going across the internet to get my web server that must have my web server online will need to know that this particular WCF Service is online. I need an example of how this client on a background thread will be able to do a polling of just "WCF Service.., Are You There?" This way our client application can notify clients before they invest a lot of time in building up work client-side to only be frustrated with the WCF Service being offline. Again I am looking for a simple way to check for WCF Service "Are You There?"

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• How does one search/poll all modal info in a frame automatically?

  - by user310631

  As you'll no-doubt be able to tell momentarily, I have little knowledge of the programming world. That being said, here goes.... In this scenario, there's a Java-based game that has a map of the game world oriented in an X, Y coordinate tile system. Some of the grid tiles are player cities, some are non-player locations. The game runs inside a frame in the browser, the X, Y coordinate map feature is one optional view, and the entire map is not available to view at any one time. Each grid tile has an "Onclick" event and an "Onmouseover" event. The mouseover event is a tooltip, the click event is something called a "modal" that has information specific to that tile. What I'd like to find out is: How can I poll all the grid tiles' "modal" information using some kind of script or other auto-running polling feature?

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• How do you fix "Too many open files" problem in Hudson?

  - by Randyaa

  We use Hudson as a continuous integration system to execute automated builds (nightly and based on CVS polling) of a lot of our projects. Some projects poll CVS every 15 minutes, some others poll every 5 minutes and some poll every hour. Every few weeks we'll get a build that fails with the following output: FATAL: java.io.IOException: Too many open files java.io.IOException: java.io.IOException: Too many open files at java.lang.UNIXProcess.<init>(UNIXProcess.java:148) The next build always worked (with 0 changes) so we always chalked it up to 2 build jobs being run at the same time and happening to have too many files open during the process. This weekend we had a build fail Friday night (automatic nightly build) with the message and every other nightly build also failed. Somehow this triggered Hudson to continuously build every project which failed until the issue was resolved. This resulted in a build every 30 minutes or so of every project until sometime Saturday night when the issue magically disappeared.

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• Downloading HTTP URLs asynchronously in C++

  - by Joey Adams

  What's a good way to download HTTP URLs (e.g. such as http://0.0.0.0/foo.htm ) in C++ on Linux ? I strongly prefer something asynchronous. My program will have an event loop that repeatedly initiates multiple (very small) downloads and acts on them when they finish (either by polling or being notified somehow). I would rather not have to spawn multiple threads/processes to accomplish this. That shouldn't be necessary. Should I look into libraries like libcurl? I suppose I could implement it manually with non-blocking TCP sockets and select() calls, but that would likely be less convenient.

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• Real time web site using PHP or ASP.NET

  - by Roman

  Hey Guys, I'm looking for a way to put real time features into my web site. The idea is asynchronous communication between 2 people - like a chat session. If I use the chat example - I'd like the second person to know that the first one has sent a message to him, without refreshing or doing something active on the web page. Polling is not a good idea here - so is there any other solution? the back-end could be ASP.NET or PHP (ASP.NET preferred). Help would be much appreciated, Thanks, Roman

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• cannot read but can write on serial port through Android Emulator

  - by Aad

  I am working on a program that is communicating with serial port over USB through Android emulator. emulator -qemu -serial /dev/ttyUSB0 The emulator is able to open the port and write into it. However, read is not happening. The program has a timeout for read maintained by a timer. The read happens in a separate 'read' thread. The main thread has a socketpair fd pair to signal the read-thread that the serial port is closed post timeout. In the read-thread, polling happens(poll() function call) over the 2 file-descriptors: one is serial port fd, the other is one of the socketpair. The board that I have connected to works fine with sending commands over 'cutecom' The poll never succeeds for serial port. However, poll succeeds for 'socketpair'ed fd and the thread ends on a close-signal sent from main-thread post timeout. Ouestions: Are there any special settings for read as even loop-back fails Are there differences between settings for read and write on a serial port?

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• Why a thread is aborted in ASP.NET MVC (again)?

  - by Dario Solera

  Here is what I do in a controller action: create and start a new Thread that does a relatively long processing task (~30 seconds on average, but might be several minutes) immediately return the page response so the user knows processing has started (trivially, a Json with a task ID for polling purposes). At some random point, ThreadAbortException is thrown, so the async task does not complete. The exception is not thrown every time, it just happens randomly roughly 25% of the times. Points to note: I'm not calling Response.End or Response.Redirect - there isn't even a request running when the exception is thrown I tried using ThreadPool and I got the same behavior I know running threads in ASP.NET has several caveats but I don't care right now Any suggestion?

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• Ubuntu quickly (python/gtk) - how to monitor stdin?

  - by neil

  I'm starting to work with Ubuntu's "quickly" framework, which is python/gtk based. I want to write a gui wrapper for a textmode C state-machine that uses stdin/stdout. I'm new to gtk. I can see that the python print command will write to the terminal window, so I assume I could redirect that to my C program's stdin. But how can I get my quickly program to monitor stdin (i.e. watch for the C program's stdout responses)? I suppose I need some sort of polling loop, but I don't know if/where that is supported within the "quickly" framework. Or is redirection not the way to go - should I be looking at something like gobject.spawn_async?

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• Is there such a thing as a dektop application event aggregator, similar to that used in Prism?

  - by brownj

  The event aggregator in Prism is great, and allows loosely coupled communication between modules within a composite application. Does such a thing exist that allows the same thing to happen between standalone applications running on a user's desktop? I could imagine developing a solution that uses WCF with TCP binding and running inside Windows Process Activation Service. Client applications could subscribe or publish events to this service as required and it would ensure all other listeners get notified of events as appropriate. Using TCP would enable event messages to be pushed out to clients without the need for polling, ensuring messages are delivered very quickly. I can't help but think though that such a thing would already exist... Is anyone aware of something like this, or have any advice on how it may be best implemented?

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• How to receive packets on the MCU's serial port?

  - by itisravi

  Hello, Consider this code running on my microcontroller unit(MCU): while(1){ do_stuff; if(packet_from_PC) send_data_via_gpio(new_packet); //send via general purpose i/o pins else send_data_via_gpio(default_packet); do_other_stuff; } The MCU is also interfaced to a PC via a UART.Whenever the PC sends data to the MCU, the *new_packet* is sent, otherwise the *default_packet* is sent.Each packet can be 5 or more bytes with a pre defined packet structure. My question is: 1.Should i receive the entire packet from PC using inside the UART interrut service routine (ISR)? In this case, i have to implement a state machine inside the ISR to assemble the packet (which can be lengthy with if-else or switch-case blocks). 2.Detect a REQUEST command (one byte)from the PC in my ISR set a flag, diable UART interrupt alone and form the packet in my while(1) loop by polling the UART?

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• How can I implement "real time" messaging on Google AppEngine?

  - by Freed

  I'm creating a web application on Google AppEngine where I want the user to be notified a quickly as possible after certain events occour. The problem is similar to say a chat server in that I need something happening on one connection (someone is writing a message in a chat room) to propagate to a number of other connections (other people in that chat room gets the message). To get speedy updates from the server to the client I'm planning on using long polling with XmlHttpRequest, hoping that AppEngine won't interfere other than possibly restriing the timeout. The real problem however is efficient notification between connections on AppEngine. Is there any support for this type of cross connection notification on AppEngine that does not involve busy-waiting? The only tools I can think of to do this at all is either using the data storage (slow) or memcache (unreliable), and none of them would let me avoid busy-waiting. Note: I know about XMPP support on AppEngine. It's related, but I want a browser based solution, sending messages to the users by XMPP is not an option.

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• Is there an easy way in Python to wait until certain condition is true?

  - by Checkers

  I need to wait in a script until a certain number of conditions become true? I know I can roll my own eventing using condition variables and friends, but I don't want to go through all the trouble of implementing it, since some object property changes come from external thread in a wrapped C++ library (Boost.Python), so I can't just hijack __setattr__ in a class and put a condition variable there, which leaves me with either trying to create and signal a Python condition variable from C++, or wrap a native one and wait on it in Python, both of which sound fiddly, needlessly complicated and boring. Is there an easier way to do it, barring continuous polling of the condition? Ideally it would be along the lines of res = wait_until(lambda: some_predicate, timeout) if (not res): print 'timed out'

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• Java reduce CPU usage

  - by steve

  Greets- We gots a few nutters in work who enjoy using while(true) { //Code } in their code. As you can imagine this maxes out the CPU. Does anyone know ways to reduce the CPU utilization so that other people can use the server as well. The code itself is just constantly polling the internet for updates on sites. Therefore I'd imagine a little sleep method would greatly reduce the the CPU usage. Also all manipulation is being done in String objects (Java) anyone know how much StringBuilders would reduce the over head by? Thanks for any pointers

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• Pushing notifications to a JavaScript?

  - by Michael Stum

  I'm just wondering if there is a way to have a server push information to a JavaScript function. Essentially I have a Dashboard-type page that has a javaScript function to get updates from the server and update the dashboard. I would like my server to be able to "ping" the JS. I don't even know how that could be possible (I'm guessing Twitter and Facebook use polling?), but I'd thought I ask. I heard of Comet, but I don't know if that works with a plain standard IIS 7 installation? (It's a SharePoint 2010 site if that matters in any way) If I understand it correctly, Comet is essentially a constantly open connection, so it seems like it's actually the opposite of what I want (reducing # of requests and therefore load)

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• How would you create a notification system like on SO or Facebook in RoR?

  - by Justin Meltzer

  I'm thinking that notifications would be it's own resource and have a has_many, through relationship with the user model with a join table representing the associations. A user having many notifications is obvious, and then a notification would have many users because there would be a number of standardized notifications (a commenting notification, a following notification etc.) that would be associated with many users. Beyond this setup, I'm unsure how to trigger the creation of notifications based on certain events in your application. I'm also a little unsure of how I'd need to set up routing - would it be it's own separate resource or nested in the user resource? I'd find it very helpful if someone could expand on this. Lastly, ajax polling would likely improve such a feature. There's probably some things I'm missing, so please fill this out so that it is a good general resource.

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• Developing a high-performance, scalable Comet application

  - by Rob

  Well, the title says most of it. I'm looking to develop a chat application that will hopefully become something more, and currently I'm considering my options for what I should build it on top of. I've taken a look at Tornado with Redis as my primary option - Tornado, being a Comet server, is perfect for long polling to retrieve the messages on Redis, which I have the intention of using as both a persistent data store, as well as a message queue with its nifty subpub features. However, I've also heard good things about Django, RabbitMQ, MongoDB and Orbited. JavaScript isn't a big problem for me, so Orbited's JavaScript support isn't too much of a boon. Really, I'd probably be happy to develop on the route I've chosen for myself, but if there are any gaping deficiencies in my plan, I'd like some kind person to point them out before I find I've wasted months on this.

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• which language to choose for a LIVE web application?

  - by fayer

  i want to create not only a web application, but a web application where everything is LIVE. eg. if someone posts a message and then another one replies, then the creator will get on his webpage a notification. and also i want to implement a chat in the web application. i want these features to be implemented using true server-push (no javascript polling)! because i only want to create web applications i don't think i will use java. i wonder if i should use python, ruby or php for this? thanks

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• Implementing a server side push for a small number of clients

  - by Helper Method

  For an web application I am working on I have the following requirements: Clients need to be able to log in via a web brower. After logging in, they will be able to change configurations (normal request/response) will be able to receive alarms sent by the server (a server side push) Now, the question is how to implement the alarms. I first thought of using some long polling approach (Comet), but as the amount of clients will definitely belimited to 5-10, I'm now thinking to go with a simpler approach. What are the options I have? Would it be okay to just let the clients poll the server? Important aspects are: Alarms should be delivered in (nearly) real-time. Alarms must not get lost (a lost alarm could cause harm to real people).

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